QSFP28 CWDM4 vs. QSFP28 PSM4: Which One is More Cost-Effective?

Although a series of 200G or even 400G optical transceiver products emerge in the optical communication market, and they have not yet been put into commercial use currently due to that they are still in the stage of preparation in some aspects. Thus, 100G optical transceiver modules, especially QSFP28 PSM4 and QSFP28 CWDM4, are still spoiled in various application fields. Well, for these two optical transceivers, what are their differences and which one is better? The answers will be found in this article.

A Brief Introduction to QSFP28 PSM4 Optical Transceiver

PSM4, the abbreviation of Parallel Single Mode 4-channels, an optics with parallel technology, defined by the 100G PSM4 MSA(Multi-Source Agreement). It uses four lanes of the parallel single fiber to deliver serialized data at a rate of 25Gbps per lane. 100GE PSM4 QSFP28 will be the optical transceiver that enables single-mode fiber to become popular in next-generation data centers due to its low cost and high configurability.

Each laser doesn’t need a MUX/DEMUX but it does need a directly modulated DFB laser (DML) or an external modulator for each fiber. QSFP28 100G PSM4 uses eight fibers, in which four fibers are for transmitting and four fibers are for receiving. A PSM4 QSFP28 optical module supports link lengths of up to 500 meters over single-mode fiber with 12 fiber MTP/MPO connectors. The light source of the QSFP 100G PSM4 optic module is a single uncooled distributed feedback (DFB) laser operating at 1310nm.

A Brief Introduction to QSFP28 CWDM4 Optical Transceiver

The QSFP28 100G CWDM4 optical transceiver is a full duplex, photonic-integrated optical transceiver module that provides a high-speed link with a maximum transmission distance of 2km for 100G Ethernet. 100G QSFP CWDM4 is designed for optical communication applications compliant with the QSFP MSA, CWDM4 MSA and portions of IEEE P802.3bm standard. CWDM4 interfaces with LC duplex connectors. It converts 4 input channels of 25Gb/s electrical data to 4 channels of CWDM optical signals and then multiplexes them into a single channel for 100Gb/s optical transmission.

Specifically speaking, four lanes with center wavelengths of 1270nm, 1290nm, 1310nm and 1330nm are controlled on the transmitting end. On the receiving end, four lanes of optical data streams are optically de-multiplexed by an integrated optical demultiplexer. With an optical multiplexer and de-multiplexer, one just uses a duplex single-mode fiber to connect two 100G CWDM4 optical transceivers.

QSFP28 CWDM4 vs. QSFP28 PSM4: Which One Is More Cost-Effective?

After knowing the basic information of PSM4 QSFP28 and CWDM4 QSFP28 optical transceiver, the comparison between them will be made in the following content to know which one is better. It is mainly made from perspectives of similarities and differences, shown as below:

Similarities of QSFP28 CWDM4 and QSFP28 PSM4 Optical Transceiver:

1. Optic Fiber Types: Both 100G QSFP CWDM4 and 100G QSFP PSM4 use single-mode fiber to transmit.

2. The Number of Lane: Both of 100G QSFP28 CWDM4 and 100GE PSM4 QSFP28 use 4 lanes(4×25Gbps) to achieve 100Gbps.

3. Wavelength: The wavelength of QSFP28 100G CWDM4 and QSFP28 100G PSM4 is around 1310 nm.

Differences of QSFP28 CWDM4 and QSFP28 PSM4 Optical Transceiver :

1. Connector Types: QSFP-100G-CWDM4-S optical transceiver is with LC duplex connector, while QSFP-100G-PSM4-S optics is with MTP/MPO connector.

2. Transmission Distance: The transmission distance of 100G QSFP CWDM4 optics is longer than that of QSFP 100G PSM4 optics. The maximum transmission distance of CWDM4 QSFP28 and PSM4 QSFP28 are respectively 2kms and 500ms.

3. Cost: QSFP28 CWDM4 optical transceiver module is more expensive than QSFP28 PSM4 optical transceiver module. It is on account that CWDM4 QSFP28 optics needs 4-wavelengths coarse wavelength division multiplexer(high in cost) while PSM4 QSFP28 optics do not need.

The Number of Optic Fiber: QSFP28 CWDM4 uses 2 single-mode fibers to transmit while QSFP28 PSM4 uses 8 single-mode fibers for transmission.

qsfp28-psm4-vs-qsfp28-cwdm4As the components such as multiplexer/demultiplexer for the CWDM4 QSFP28 optical transceiver are very expensive, the cost of 100G QSFP28 CWDM4 optical module is much higher than that of 100G QSFP28 PSM4 optical module. It is seen from the above information that QSFP28 PSM4 seemingly is a more cost-effective choice than QSFP28 CWDM4. However, if the cost is taken into account from the perspective of the whole 100G connection, it should actually depend on the link distance. For PSM4 QSFP28 optics, as the connection distance increases, its total cost climbs up very fast due to the increase in the number of optic fibers. Therefore, 100GE PSM4 QSFP28 optics is a recommended solution with cost-effectiveness for the deployment of 100G network with a short reach. On the contrary, if it is to deploy a 100G network with long-reach, 100GE CWDM4 QSFP28 is the better choice.


It is believed that the answers about what the differences between 100G QSFP28 CWDM4 and 100G QSFP28 PSM4 optical module are and which one is better are very clear.

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